Harry Siroka has spent nights on a park bench, in the back room of a bar and on the seat of a rented car. He has been accosted by a man swinging a cane. He has had dirt kicked in his face in front of 4,000 people.

Siroka is a minor league baseball umpire.

The 27-year-old Brooklyn, N.Y. native is one of six umpires who call the games of the Alexandria Dukes in the Class A Carolina League. This season each will travel more than 10,000 miles between Northern Virginia and North Carolina - chasing a dream.

Their hope is to become one of the 52 umpires in the major leagues. Siroka and his partners, all in their mid-20s, know their chances are slim. More than 100 others are ahead of them in Class AA and AAA leagues throughout the nation. Only a handful of all 143 umpires in the minors will ever get to call a big-league ball or strike.

But each spring, they leave their families, friends and part-time jobs to live with inconvenience, insults and 400-mile road trips.

For years, Siroka entertained hopes of breaking into the big leagues as a player. So did his partners, Rich Humphrey of Paramus, N.J. and Tim Clapp of Orlando, Fla. Each recognized his own athletic limitations and gradually began the shift to umpiring - little leagues, college and later sandlot games. Then in February 1975 they did what all aspiring umpires do. They went to Florida to attend umpires school.

Siroka, Humphrey and Clapp were among 150 others who paid the $700 tution to enroll in the five-week program in St. Petersburg. They were three of the 10 hired that year.

"The guys who made it were the ones who showed they could be assertive and take the pressure," said Clapp, 26, a banker in the off season. "Believe me, a lot of people try to push you around. You have to be tough. You stand your ground and ignore it. If they keep pushing, you can always throw them out of the games."

But ejecting an unruly manager or player and getting him peacecable off the field are frequently two different matters in the bush leagues.

"I tossed a manager out of the game in the first game I ever upired in Class A," Siroka said. "My only mistake was to turn my back on the guy before he left the field. I was bending down to brush off the plate and he snuck around me and kicked a mound of dirt in my face. The whole stadium began to cheer. All I could do was put it in my report to the league office."

Mike Holoka, the youngest umpire in the minors at 24, couldn't budget Duke Manager Les Peden after ejecting him earlier this season. Holoka delivered a total of six thumbs, but Peden merely leaned against the dugout with a smile on his face. Holoka then borrowed a pocket watch and ordered the stubborn skipper to leave in 60 seconds. Peden let 50 elapse before beginning a leisurely stroll down the field, doubling back through the stands to the applause of Duke fans.

When the Carolina League umpires aren't contending with the players and managers, their ears are burned by unflattering comments from the bleachers.

"Anyone who says he doesn't hear them is lying," Clapp said.

"You can go crazy sitting around a strange hotel room all day in a town you know nothing about" said Humphrey, who works as a substitute teacher in the winter. "It's hard for me because I'm married and have an 8-year-old son. When I finally brought him to watch a game in Alexandria, he really got upset and began to scream at all the fans who were giving me a hard time."

Sometimes, after a long day's drive, it's impossible to find a hotel room. Last month Joe Conley, another umpire, had to spend the night on the floor of an empty school next to Alexandria's Four Mile Run Park.

But often the hardest thing about umpiring in Class A is the uncertainty. Your good performances may go totally unnoticed. You never know when you are being scouted and evaluated by representatives of the Minor League Umpire Development Program. You wait - usually for years - for word of a promotion. Sometimes it never comes.

"I think all of us have set some kind of time limit on this," said Holoka, who began umpiring Class A in 1974.

Last week, after umpiring a night game in Alexandria, he got a telephone call at his motel room. The Class AA Southern League needed a new umpire and wanted him to start right away in Jacksonville, Fla. Holoka packed his suitcase and in two hours was on a midnight flight heading south - one step closer to catching his dream.